Guidelines for Setting Pnoise/HBnoise Sidebands to Get Accurate Results

5 Aug 2011 • 2 minute read

I get quite a few questions from designers along the lines of "How do I set the number of pss/hb harmonics and pnoise/hbnoise sidebands in order to get accurate results?" Here are some general guidelines that I follow:

The number of sidebands (harmonics) in the simulation can affect performance.

When using pnoise/hbnoise, the upper frequency to be considered for noise folding is set by the Maximum sideband term. The number of Sidebands that you specify corresponds to the set of periodic small signal output frequencies of interest. For instance, setting the Maximum sideband lets you specify the number of frequency conversion terms to take into account.

PSS shooting takes 20 timepoints at the highest harmonic specified. In general, use 1/4 the number of harmonics as the number of sidebands. So, if you specify 7 harmonics, use up to 28 sidebands.. (There is a minimum of 200 points in the PSS analysis. You need 5 timepoints at the frequency of the highest sideband in the analysis).

If maxsidebands is less than 40, you shouldn't need to worry about increasing harmonics. If you have greater than 40 sidebands, either:

a. Set maxacfreq to the number of sidebands*PSSfund

-- or --

b. Set the number of PSS harmonics to the number of pnoise sidebands divided by 4.

As an example, say that you want 80 sidebands. Set the number of harmonics to 80/4=20 harmonics.

PSS-HB and HB analyzes such that only the harmonics specified are calculated. The pnoise Maximum sideband needs to be set to the same number as harmonics in the HB analysis. In MMSIM 7.2 and IC614isr2 or later, this is the default when the Maximum sideband field is left blank. Based on this, select a reasonable number of harmonics and sidebands, run your pss/pnoise (or hb/hbnoise) analysis. Then, increase your harmonics/sidebands and rerun the simulation. If your pnoise or hbnoise answer changes, you need more harmonics/sidebands.

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Have fun simulating!

best regards,

Tawna Wilsey